1. Field of the Invention
The invention relates generally to fiber placement technology, and more specifically, to a compaction device with interdependent segments that are movable relative to one another so as to enable conformity with an irregular surface during fiber placement.
2. State of the Art
Fiber placement machines and techniques are well known in the art and enjoy considerable usage in the production of composite parts or structures. Composite structures are particularly useful in high performance applications, such as in the aerospace industry because of their high strength to weight ratio, good corrosion resistance, good impact resistance, and high electrical and thermal resistance exhibited by composite parts. As such, composite components are frequently replacing metallic components in various structures, apparatuses and systems.
In producing composite components, fiber placement machines are capable of individually and selectively feeding and cutting separate fiber bundles or tows so as to form a fiber band on a surface of the part. This selective cutting and feeding of tows advantageously enables the fiber compaction device to put down the tows in an arcuate path on the part surface that prevents buckling, wrinkling or misalignment of fibers. The fiber tows, also known as tow pregs, are generally a bundle of continuous fibers impregnated with a resin (i.e., a polymeric material that may be in a cured, uncured, or partially cured state).
One example of a fiber placement machine includes a compaction device comprising a plurality of roller segments disposed in a side-by-side relationship, each roller being supported for pivotable movement about an eccentrically disposed pivot shaft. The roller segments are movable independent of one another such that the compaction device can conform to surface geometries while attempting to apply a pressure against the individual tows as they are pressed onto the surface of a mandrel or underlying layer of a given part. Such prior art compaction devices commonly employ a fixed centermost roller segment while the other segments are permitted to move in and out, being pushed forward by pneumatic pressure or spring force while being able to slide as an assembly. Such a device is described in U.S. Pat. No. 5,454,897 issued to Vaniglia.
Some compaction devices having independently movable segments incorporate the use of pressure bladders (i.e., fluid pressurized elastic chambers), for example one bladder on each side of the fixed center segment, to apply a compaction force to the roller segments. The bladders urge the associated roller segments pivotally in the fore direction, relative to the fixed center segment, in an attempt to conform with the surface geometry of the part and to provide a generally uniform pressure against the surface.
One problem with prior art compaction devices using a fixed centermost roller segment is that the segments must be balanced so that the force exerted by each roller segment is the same. Additionally, with a fixed center segment, the conformability of the roller system to complex geometric surfaces is rather limited. Furthermore, because the segments work independently of one another, there is nothing to keep the average segment position at the nominal position (i.e., the position of a segment when there is no displacement from the center shaft).
In fiber placement compaction devices using inflatable bladders, many additional problems exist. For example, when the bladder pressure is too low, the center segment carries a higher load. This can ultimately result in damage to the center segment, to the part being fabricated (for example, if fiber is being placed over core), or both. This is particularly a problem when the bladders fail to inflate, as such an event could result in irreparable damage to the rollers which are expensive to replace.
On the other hand, if the bladders are over-inflated, the center section may lift completely off the surface of the composite part, thereby resulting in failure to compact one or more tows that are being laid on the surface of the part. Thus, bladders require pressure regulation and continuous inflation. Therefore, the bladders require an opening through which the gas can enter and exit and a sealed system to supply the pressurized gas. These sealed connections have often breached such that they have to be resealed, which is a time consuming operation. In general, bladders require costly maintenance and repair that may include disassembly of the roller.
Therefore, it would be desirable to provide an enhanced fiber placement compaction device. For example, a need exists for improving the positioning and balancing of segment forces, increasing the conformability of the roller segments, and simplifying the maintenance and control of a compaction device.